Infinite hybrid metal-ligand networks built from metal connectors and bridging ligands are known as "coordination polymers" or "MOFs" ( Metal Organic Frameworks). Although some of them, such as Prussian blue, a mixed-valence iron cyanide, were discovered by serendipity as early as the 18th century(Prussian blue was discovered in 1704 by German colorists), these materials have been attracting a great deal of interest from the scientific community over the last fifteen years. Indeed, the birth of reticular chemistry in the late 80s and the implementation of a genuine engineering of coordination polymers by soft chemistry have led to the discovery of new crystalline, highly porous "MOFs" with a wide variety of chemical compositions, since the nature of the metal cation (Zn, Co, Cr, Fe, Cu, etc.) and the organic bridging ligand can be infinitely varied. The latter can be anionic, neutral or mixed (di- or polyacids, di- or polyamines, etc.). This research has opened up a new field of investigation, rich in possibilities and perspectives, in which the chemist's imagination can express itself to the full.
Their high porosity, adjustable pore size, the dynamics of certain hybrid structures and the variety of accessible topologies and architectures give MOFs remarkable physical properties, making them ideal for applications in a wide range of fields. This lecture retraces the history of these coordination polymers, while discussing their mode of construction, the strategies developed by the main teams in the field and the main physical properties currently being studied. Among the many coordination polymers, we have focused on MOFs based on zinc and carboxylate or imidazolate ligands, MILs (materials from the Lavoisier Institute) based on carboxylates and transition metals (iron, chromium, vanadium) and PCPs(Porous Coordination Polymers) based on copper, zinc and a combination of acid and basic ligands (terephthalic acid and triethylene diamine). This choice has enabled us to illustrate simply the different modes of construction starting from isolated cations or oxo-metallic clusters, the possible post-functionalization of the materials obtained, the host network-guest molecule interactions and the dynamics of certain hybrid frameworks generated during the adsorption process. In the field of gas adsorption in particular, MOFs, MILs and other compounds are highly effective adsorbers, as they can store large quantities of hydrogen,CO2 and methane. Although the results reported in this field seem highly promising for gas purification and separation, they are still the subject of much controversy. An objective comparison of the various studies highlights the need for standardized tests, as porosity activation processes are not always optimized, and particle size and morphology can vary from one study to another, altering the specific surface areas and accessibility of the adsorbate to the materials' active sites. Furthermore, in addition to temperature and pressure conditions, control of the purity of the gases used (presence of traces of water) seems essential in order to be able to truly compare the performance and stability of these materials. We also emphasized the possibilities offered by these hybrid porous structures, in which pore size, shape, surface functionality and channel length can be tailored to develop confined-space chemistry, enabling, for example, better control of polymerization processes to obtain organic polymers with less mass polydispersity, stereoregularity or, in the case of copolymers, more homogeneous sequencing of the different monomers.
In this lecture, we also presented the many properties of these coordination polymers, focusing on their catalytic properties, their selectivity for sensor applications, and recent developments in biomedical applications. These new materials are being tested as therapeutic vectors for the controlled release of active ingredients and for nuclear magnetic resonance imaging. Today, some MOFs are synthesized on an industrial scale, with production of the order of a ton a day, and marketed by chemical product distributors. The door to this "Ali Baba" cave is open, but will we be able to exploit its riches intelligently and wisely?
